Communications technology is organised in "layers". The top layer is the application, for instance a video-conferencing system. The bottom layer is the physical technology that moves the bits and bytes along a wire, fibre, etc; one example is an Ethernet link over twisted-pair building wiring. Layers in between are responsible for tasks such as sharing a communications link between several different applications, and making sure each application's data gets to the right place.
Internet Protocol is currently the dominant technology for one of the intermediate layers. A major problem for "real-time" applications is that it does not convey to the lower layers any details of the service the application needs. For instance, the video conferencing system will be sending packets of audio and video data at regular intervals, and it needs to be sure they will all be delivered promptly if it is to keep delays (which have a major effect on how "natural" the conversation is between participants in the conference) to a minimum. The lower layers may well be able to provide such guarantees, but in today's Internet the IP layer does not provide a way for them to know what the application's requirements are, and the application cannot discover details of the service the lower layers can provide.
Flexilink allows the lower layers to "see" details of the requirements of real-time applications, and reports back to the application details of the service that will be provided. It also allows applications which do not need this facility to continue to use IP.
With Internet Protocol, every packet must contain all the information needed to get it to its destination. This can amount to a significant overhead in both data and processing effort within the network, and to reduce this overhead most audio applications batch up their data so they can send larger, less frequent, packets, thus further increasing the delays.
Flexilink separates out the tasks of choosing the route and forwarding the data, which dramatically reduces the size of headers and also simplifies the design of switching equipment.
Many of the protocols used on IP networks find the resources an application needs by sending out a "broadcast" message and waiting (typically several seconds) to see what replies are received. If no reply is received, there is no indication of the reason for the failure. When sending a message on an IP network, the only information on its progress through the network is in the reply (or lack of one) from the far end. If a media stream is interrupted, there is no indication whether this is because of a problem in the sender, failure of a link within the network, or delays due to congestion.
Flexilink units locate resources by asking neighbouring units, so receive an immediate response which, if negative, indicates where the problem is. Link failures are reported as soon as they occur, and media flows through links that fail are re-routed immediately.
Because Flexilink headers do not include addresses, a much more flexible form of addressing is possible than with other protocols; for instance, domain names can be used directly rather than having to be translated into IP addresses.
Communication with network management stations uses IEC62379, the international standard Common Control Interface. This provides a convenient way of managing applications running over the network and of monitoring the operation of the network including giving immediate notification of hardware faults and collecting statistics showing where bottlenecks are occurring in the network. However, no manual intervention or configuration is required in the management of the network.
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